Esther Inglis-Arkell

We all love that famous movie tagline, but it can be tough for kids to understand. Here's a basic experiment you can do with kids — or for your own curiosity — to demonstrate exactly how a vacuum can eliminate sound. All it takes is a bottle, a bell, and a couple of matches. Try it out!

Ah, that first Alien film, when no one knew about killer robots and eggs that explode into face-hugging monsters yet. It was a more innocent time, and the movie's slogan is burned into all our brains: "In space, no one can hear you scream." That might not go over so well with the kiddies, so maybe you can gentle it to, "In space, no one can hear you ring a bell." And you can prove it to be true.

All you need is to grab one of those leftover bells from a Christmas decoration and tie it to a string. Tape the string to the inside of a plastic bottle lid, so that the bell hangs down inside the bottle when the lid is screwed on. The plastic should be of a more rigid sort than your typical water bottle. (The recommendation is a Snapple bottle.) Get something that will retain its shape. Screw down the cap and ring the bell. You should be able to hear it just fine. Unscrew the cap and open it up again.

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Now grab a couple of matches, light them, and put them inside the bottle. Immediately screw the cap back on and let the matches burn down. Wait until the bottle is cool, and shake it again. The bell is going to sound faint. Get the right amount of matches, or burning piece of paper, and you may quiet it altogether.

The matches consume the oxygen in the air. What's left inside the bottle, after they've burned down to nothing, is a slight vacuum. It won't be powerful, but it should be enough that the sound will be fainter without enough gas to move through as effectively.